Liquid conductivity detectors in the related art have been used to measure a contamination level of drinking water, purity of water for a boiler, a contamination level of lubricant in heavy machinery, performance of a battery electrolyte, a concentration of a chemical material in a fluid analysis system, and the like.
Since liquid conductivity in the applications, in general, has relatively high values, the conductivity detectors is configured of a conductivity sensor configured to operate at room temperature and a detection circuit constructed using an open loop signal generator and a asynchronous demodulator easily fabricated.
A sensor and an apparatus for measuring electric conductivity are disclosed in Korean Patent No. 10-741042 (2007 Jul. 12).
In the sensor for measuring electrical conductivity which measures electrical conductivity in water, a sensor and an apparatus for measuring electric conductivity in the related art as illustrated in FIG. 1 includes a voltage generating circuit 400 for generating an electrical signal having a predetermined frequency and amplitude, an output electrode 302 for outputting the electrical signal supplied from the voltage generating circuit 400; one or more compensation electrodes 304 and 306 for receiving the electrical signal from the output electrode 302; a compensation-electrode compensating circuit 404 for compensating the electrical signal applied from the voltage generating circuit 400 to the output electrode 302; an input electrode 308 for receiving the electrical signal from the output electrode 302; a current measuring circuit 406 for detecting the electrical signal received in the input electrode 308; and a signal amplification and processing circuit 408 for amplifying and processing the current signal and transmitting the processed signal to an external apparatus in a remote place.
The detector in the related art has problems in that considerable fluctuations of a baseline as a reference for the measurements and measured conductivity, due to noise effects by asynchronous detection, unstability of a reference signal, and difficulty in constantly mataining the temperature of a conductivity sensor. Therefore, theses variations become factors that limit a dynamic range in conductivity measurement of liquid including an infinitesimal amount of ions. Further, due to these problems, the conductivity detector in the related art is difficult to be used in conductivity measurement of liquid having an infinitesimal ion concentration.